Power system with multiple generator units

ABSTRACT

A method of operating a power system is provided, the power system having power-system controls. The method may include automatically setting a priority ranking for a plurality of generator units of the power system with the power-system controls based at least in part on an operating parameter of each generator unit indicative of a quantity of work done by the generator unit. The method may also include automatically controlling which of the generator units run with the power-system controls based at least in part on the priority ranking of the generator units.

TECHNICAL FIELD

The present disclosure relates to power systems and, more particularly, to power systems with multiple generator units for supplying electricity.

BACKGROUND

Many power systems have multiple generator units for supplying electricity to one or more electric power loads. When the electric power loads of such a power system have relatively low electricity requirements, the power system may operate more efficiently by running a subset of the generator units than by running all of the generator units at a low power output level. Unfortunately, running some generator units while not running other generator units may cause the running generator units to accumulate more service than the generator units not running.

Published U.S. Patent Application No. 2006/0266256 to Donnelly et al. (“the '256 application”) discloses a method of controlling how many of a plurality of generator units of a locomotive run based on power needs of the locomotive, and the '256 application suggests balancing the usage of the generator units' engines. The locomotive disclosed by the '256 application has the plurality of generator units connected in parallel to a DC bus. The locomotive further includes a plurality of traction motors connected in parallel to the DC bus so that they may receive electricity supplied to the DC bus by the plurality of generator units. The '256 application teaches that the control system of the locomotive may determine how many of the generator units to run by determining the amount of power required for the traction motors, dividing the determined power requirement by the power rating of each generator unit, and rounding up. The '256 application suggests that the control system of the locomotive may use engine logs for the generator units to balance usage of the different generator units' engines.

Although the '256 application suggests using engine logs to balance operation of the engines of multiple generator units of a locomotive, certain disadvantages persist. For example, the '256 application does not disclose how to actually coordinate operation of the generator units based on the engine logs to balance usage of the generator units' engines.

The power system and methods of the present disclosure solve one or more of the problems set forth above.

SUMMARY OF THE INVENTION

One disclosed embodiment relates to a method of operating a power system, the power system having power-system controls. The method may include automatically setting a priority ranking for a plurality of generator units of the power system with the power-system controls based at least in part on an operating parameter of each generator unit indicative of a quantity of work done by the generator unit. The method may also include automatically controlling which of the generator units run with the power-system controls based at least in part on the priority ranking of the generator units.

Another embodiment relates to a method of operating a power system, the power system having power-system controls. The method may include automatically controlling with the power-system controls which of a plurality of generator units of the power system run. This may include selecting which of the generator units run based at least in part on an operating parameter indicative of an amount of service accumulated by each generator unit since a reference point in time, the reference point in time being a time other than the time the generator unit first ran.

A further embodiment relates to a mobile machine. The mobile machine may include a plurality of generator units and one or more electric propulsion motors. Additionally, the mobile machine may include power-system controls that control the plurality of generator units and the one or more electric propulsion motors, which may include selectively operating the mobile machine in a first operating mode. Operating the mobile machine in the first operating mode may include running a plurality of the generator units upon entering the first operating mode, regardless of the electricity requirements of the mobile machine. The power-system controls controlling the plurality of generator units and the one or more electric propulsion motors may also include selectively propelling the mobile machine at least in part by operating one or more of the one or more electric propulsion motors with electricity generated by one or more of the plurality of generator units.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic illustration of one embodiment of a machine that includes a power system according to the present disclosure;

FIG. 2A is a flow chart illustrating one embodiment of a control method according to the present disclosure;

FIG. 2B is a flow chart illustrating one of the processes of the flow chart of FIG. 2A in greater detail;

FIG. 2C is a flow chart illustrating another of the processes of the flow chart of FIG. 2A in greater detail;

FIG. 2D is a flow chart illustrating another of the processes of the flow chart of FIG. 2A in greater detail;

FIG. 2E is a flow chart illustrating another of the processes of the flow chart of FIG. 2A in greater detail;

FIG. 3A is a chart illustrating one embodiment of a lookup table for use in a control method according to the present disclosure;

FIG. 3B is a chart illustrating one embodiment of another lookup table for use in a control method according to the present disclosure; and

FIG. 3C is a chart illustrating one embodiment of another lookup table for use in a control method according to the present disclosure.

DETAILED DESCRIPTION

FIG. 1 illustrates a machine 10 having a power system 12 according to the present disclosure. Power system 12 may include one or more electric power loads 14, a plurality of electric power sources 16, a power-transfer system 17 for transferring electricity from electric power sources 16 to electric power loads 14, and power-system controls 18. Electric power loads 14 may include a first set of one or more electric power loads 24 and a second set of one or more electric power loads 26.

Depending on the role that machine 10 serves, the one or more electric power loads 14 of power system 12 may include various types of components. In some embodiments, machine 10 may be a mobile machine, and the first set of electric power loads 24 may include one or more electric propulsion motors 20 drivingly connected to one or more propulsion devices 22 for propelling machine 10. In some embodiments, machine 10 may be a railroad locomotive. Electric propulsion motors 20 may include any type of electric motors. In some embodiments, electric propulsion motors 20 may be DC motors. Propulsion devices 22 may include any types of components operable to propel machine 10 by receiving mechanical power from electric propulsion motors 20 and applying at least a portion of that power to the environment around machine 10. For example, as FIG. 1 shows, propulsion devices 22 may be wheels. In embodiments where machine 10 is a railroad locomotive, propulsion devices 22 may be wheels configured to ride on and apply power to rails.

The second set of electric power loads 26 may include any types of components that use electricity. For example, the second set of electric power loads 26 may include lights, heating and/or cooling devices, air compressors, pumps, actuators for moving various components of machine 10, and/or various other types of electric components.

Electric power sources 16 may include a plurality of generator units G_(A), G_(B), G_(C). Each generator unit G_(A), G_(B), G_(C) may include any component or components operable to supply electricity. In some embodiments, each generator unit G_(A), G_(B), G_(C) may include a power source PS_(A), PS_(B), PS_(C) and at least one electric generator drivingly connected to the power source PS_(A), PS_(B), PS_(C). Each power source PS_(A), PS_(B), PS_(C) may be any type of component operable to produce mechanical power, including, but not limited to, a diesel engine, a turbine engine, a gasoline engine, or a gaseous-fuel-driven engine. In some embodiments, each generator unit G_(A), G_(B), G_(C) may have drivingly connected to its power source PS_(A), PS_(B), PS_(C) an electric generator EG_(A1), EG_(B1), EG_(C1) for supplying electricity to the first set of electric power loads 24. Additionally, each generator unit G_(A), G_(B), G_(C) may have drivingly connected to its power source PS_(A), PS_(B), PS_(C) another electric generator EG_(A2), EG_(B2), EG_(C2) for supplying electricity to the second set of electric power loads 26.

Each electric generator EG_(A1), EG_(B1), EG_(C1), EG_(A2), EG_(B2), EG_(C2) may be any type of component configured to receive mechanical power from the associated power source PS_(A), PS_(B), PS_(C) and convert at least a portion of that mechanical power into electricity. For example, electric generators EG_(A1), EG_(B1), EG_(C1), EG_(A2), EG_(B2), EG_(C2) may include one or more AC induction generators, one or more permanent-magnet generators, one or more AC synchronous generators, and/or one or more switched-reluctance generators. In some embodiments, one or more of electric generators EG_(A1), EG_(B1), EG_(C1), EG_(A2), EG_(B2), EG_(C2) may be different kinds of electric generators. For example, electric generator EG_(A1) may be one type of electric generator, and electric generator EG_(A2) may be another type of electric generator.

Each generator unit G_(A), G_(B), G_(C) may also include one or more control components. For example, each electric generator EG_(A1), EG_(B1), EG_(C1), EG_(A2), EG_(B2), EG_(C2) may include a power electronics module. The power electronics module of each electric generator EG_(A1), EG_(B1), EG_(C1), EG_(A2), EG_(B2), EG_(C2) may control excitation current of the electric generator EG_(A1), EG_(B1), EG_(C1), EG_(C1, EG) _(B2), EG_(C2), thereby controlling one or more aspects of the electricity generated by the electric generator EG_(A1), EG_(B1), EG_(C1), EG_(A2), EG_(B2), EG_(C2).

Additionally, to regulate the flow of electricity from electric generators EG_(A1), EG_(B1), EG_(C1), EG_(A2), EG_(B2), EG_(C2) to power-transfer system 17, each generator unit G_(A), G_(B), G_(C) may include a power regulator PR_(A1), PR_(B1), PR_(C1) for its electric generator EG_(A1), EG_(B1), EG_(C1) and a power regulator PR_(A2), PR_(B2), PR_(C2) for its electric generator EG_(A2), EG_(B2), EG_(C2). Each power regulator PR_(A1), PR_(B1), PR_(C1), PR_(A2), PR_(B2), PR_(C2) may be any type of device configured to regulate one or more aspects of the transfer of electricity from the associated electric generator EG_(A1), EG_(B1), EG_(C1), EG_(A2), EG_(B2), EG_(C2) to power-transfer system 17. Each power regulator PR_(A1), PR_(B1), PR_(C1), PR_(A2), PR_(B2), PR_(C2) may, for example, include a rectifier for converting multiphase AC electricity generated by the associated electric generator EG_(A1), EG_(B1), EG_(C1), EG_(A2), EG_(B2), EG_(C2) into DC electricity. In some such embodiments, the rectifier of each power regulator PR_(A1), PR_(B1), PR_(C1), PR_(A2), PR_(B2), PR_(C2) may include diodes that allow electricity to flow from the associated electric generator EG_(A1), EG_(B1), EG_(C1), EG_(A2), EG_(B2), EG_(C2) to power-transfer system 17, but not in the opposite direction. Power regulators PR_(A2), PR_(B2), PR_(C2) may also be operable to control the voltage of the electricity supplied to power-transfer system 17 by electric generators EG_(A2), EG_(B2), EG_(C2).

Each generator unit G_(A), G_(B), G_(C) may also include a power-source controller C_(PSA), C_(PSB), C_(PSC). Power-source controllers C_(PSA), C_(PSB, C) _(PSC) may each include one or more processors (not shown) and one or more memory devices (not shown). Each power-source controller C_(PSA), C_(PSB), C_(PSC) may control whether the generator unit G_(A), G_(B), G_(C) it belongs to runs by controlling whether the associated power source PS_(A), PS_(B), PS_(C) runs. Each power-source controller C_(PSA), C_(PSB), C_(PSC) may also control various other aspects of the operation of the associated power source PS_(A), PS_(B), PS_(C), including, but not limited to, its operating speed and power output. Accordingly, each power-source controller C_(PSA), C_(PSB), C_(PSC) may monitor various operating parameters of the associated power source PS_(A), PS_(B), PS_(C), such as its operating speed, its operating temperature, its power output, how much fuel it is consuming or has consumed, one or more aspects of the operation of its lubrication system, and/or various similar parameters. Power-source controllers C_(PSA), C_(PSB), C_(PSC) may use sensors and/or any other suitable means to monitor such operating parameters.

Power-transfer system 17 may include any component or components operable to transfer power from electric power sources 16 to the one or more electric power loads 14. For example, power-transfer system 17 may include a circuit 28 for transferring power from electric generators EG_(A1), EG_(B1), EG_(C1) to the first set of electric power loads 24 and a circuit 30 for transferring power from electric generators EG_(A2), EG_(B2), EG_(C2) to the second set of electric power loads 26. Circuits 28, 30 may be electrically isolated from one another. Power-transfer system 17 may include various provisions for regulating and/or modifying electricity supplied to electric power loads 14. For example, circuit 30 may include a power regulator PR_(L) operable to convert DC electricity received from power regulators PR_(A2), PR_(B2), PR_(C2) into AC electricity for use by the second set of electric power loads 26.

Power-system controls 18 may include any components configured to control operation of machine 10 in the manners discussed hereinbelow. Power-system controls 18 may include various components of generator units G_(A), G_(B), G_(C), power-transfer system 17, and electric power loads 14. For example, in the embodiment shown in FIG. 1, power-system controls 18 may include the power electronics modules (not shown) of electric generators EG_(A1), EG_(B1), EG_(C1), EG_(A2), EG_(B2), EG_(C2); power regulators PR_(A1), PR_(B1), PR_(C1), PR_(A2), PR_(B2), PR_(C2), PR_(L); and power-source controllers C_(PSA), C_(PSB), C_(PSC). Additionally, as FIG. 1 shows, power-system controls 18 may include a controller 38, a controller 40, an operator interface 42, and a service interface 43. Power-system controllers C_(PSA), C_(PSB), C_(PSC), controller 38, controller 40, and operator interface 42 may form a control network 37.

Each controller 38, 40 may include one or more processors (not shown) and one or more memory devices (not shown). Controller 38 may be operatively connected to each power-source controller C_(PSA), C_(PSB), C_(PSC). This may allow controller 38 to receive information about the operation of power sources PS_(A), PS_(B), PS_(C) from power-source controllers C_(PSA), C_(PSB), C_(PSC) and/or indirectly control one or more aspects of the operation of power sources PS_(A), PS_(B), PS_(C) by transmitting control signals to power-source controllers C_(PSA), C_(PSB), C_(PSC). Controller 38 may also be operatively connected to controller 40, so that controllers 38, 40 may exchange information. Controller 40 may also be operatively connected to the power electronics module of each electric generator EG_(A1), EG_(B1), EG_(C1), EG_(A2), EG_(B2), EG_(C2), so that controller 40 may control generation of electricity by electric generators EG_(A1), EG_(B1), EG_(C1), EG_(A2), EG_(B2), EG_(C2). Similarly, controller 40 may be operatively connected to each power regulator PR_(A2), PR_(B2), PR_(C2), so that controller 40 may control one or more aspects of the electricity supplied to power-transfer system 17 by electric generators EG_(A2), EG_(B2), EG_(C2), such as the voltage of the electricity.

To facilitate effective control of the supply of electricity to electric power loads 14, controller 40 may monitor various aspects of the generation of electricity by electric generators EG_(A1), EG_(B1), EG_(C1), EG_(A2), EG_(B2), EG_(C2) and/or various aspects of the transmission of electricity through power-transfer system 17. For example, controller 40 may monitor the voltage, current, frequency, and/or phase of electricity generated by one or more of electric generators EG_(A1), EG_(B1), EG_(C1), EG_(A2), EG_(B2), EG_(C2). Controller 40 may employ sensors and/or other suitable means to monitor such operating parameters. In some embodiments, controller 40 may monitor the voltage in circuit 28 with a voltage sensor 52. Controller 40 may also monitor various other aspects of the operation of machine 10 through various means. For example, controller 40 may monitor the speed of mobile machine 10 with a speed sensor 50.

Operator interface 42 may include any component or components configured to transmit operator inputs to one or more components of machine 10. In some embodiments, operator interface 42 may include components that an operator can manipulate to indicate whether the operator desires propulsion of machine 10 by electric propulsion motors 20 and, if so, in what direction and with how much power the operator desires electric propulsion motors 20 to propel machine 10. For example, as FIG. 1 shows, operator interface 42 may include a reverser 44 and a power selector 46.

Reverser 44 may have an operating state designated “FORWARD, ” which a user can select to indicate that the operator desires forward propulsion; an operating state designated “REVERSE, ” which an operator can use to indicate that the operator desires backward propulsion; and an operating state designated “NEUTRAL, ” which an operator can select to indicate that the operator does not desire propulsion of machine 10. Reverser 44 may indicate to one or more other components of power-system controls 18 which of the FORWARD, REVERSE, and NEUTRAL operating states the operator has selected. For example, reverser 44 may transmit a signal to controller 40 indicating which of these three operating states the operator has selected.

Power selector 46 may serve as a means by which the operator can indicate how much power the operator desires electric propulsion motors 20 to employ to propel machine 10. Power selector 46 may have a plurality of discrete power settings that an operator can select to indicate one of a plurality of discrete power levels that the operator desires for propulsion of machine 10. For example, as FIG. 1 shows, power selector 46 may have an “IDLE” setting and power settings 1-8. The IDLE power setting may correspond to the lowest desired power level for propulsion, and progressively higher numerical power settings may correspond to progressively higher desired power levels for propulsion. In some embodiments, rather than a plurality of discrete power settings, power selector 46 may have a continuous range of power settings that an operator may select. Power selector 46 may communicate which power setting the operator has selected to one or more other components of power-system controls 18. For example, power selector 46 may transmit a signal to controller 40 indicating the notch power setting selected by the operator.

Operator interface 42 may also include a mode selector 48 with which an operator may indicate which of a plurality of propulsion modes the operator desires. In some embodiments where machine 10 is a railroad locomotive, mode selector 48 may have a “LINE-HAUL” operating state for indicating that the operator desires a “line-haul” mode of operation and a “SWITCHER” operating state for indicating that the operator desires a “switcher” mode of operation. The line-haul mode of operation may be a mode of operation tailored for pulling railroad cars long distances. The switcher mode of operation may be a mode of operation tailored for moving railroad cars in a rail yard. Mode selector 48 may communicate to one or more other components of power-system controls 18 which mode of operation the operator has selected. For example, mode selector 48 may send a signal to controller 40 indicating whether the operator has selected line-haul mode or switcher mode.

As shown in FIG. 1, service interface 43 may be an off-board service tool that is not permanently mounted to machine 10 but configured to be readily communicatively linked to control network 37 to allow a technician to transmit communications to and receive communications from control network 37. Such a service tool may include one or more processors (not shown) and or memory devices (not shown). Service interface 43 may be configured with provisions for enabling the operator of machine 10 to command power-system controls 18 to exclude one or more of generator units G_(A), G_(B), G_(C) from operation. Accordingly, control network 37 may be configured to receive from service interface 43 a predetermined communication for indicating that the operator wishes one or more of generator units G_(A), G_(B), G_(C) excluded from operation and to thereafter store data indicating that those one or more generator units G_(A), G_(B), G_(C) should be excluded from operation. Service interface 43 is not limited to the configuration shown in FIG. 1. For example, in addition to, or in place of, an off-board service tool, service interface 43 may include one or more components mounted to machine 10 and communicatively linked to control network 37. In some embodiments, service interface 43 may include components of control network 37.

There may also be a position-information system 39 capable of providing information about the location of machine 10. Position-information system 39 may include any component or components operable to provide information about the location of machine 10. In some embodiments, position-information system 39 may include one or more components on machine 10 that interact with one or more components off board machine 10 to provide information about the location of machine 10. For example, position-information system 39 may constitute a so-called “Global Positioning System” with an information processor 41 onboard machine 10 and an off-board portion 47 that interact with one another to generate information about the location of machine 10. In some embodiments, position-information system 39 may be communicatively linked to power-system controls 18, so that position-information system 39 may communicate information about the location of machine 10 to power-system controls 18. For example, as FIG. 1 shows, information processor 41 may be communicatively linked to controller 40. Position-information system 39 may communicate with power-system controls 18 via hardwired communication lines, or position-information system 39 may communicate with power-system controls 18 without hardwired communication lines, such as via electromagnetic waves.

Alternatively, in some embodiments, position-information system 39 may not be directly communicatively linked to power-system controls 18. In some such embodiments, power-system controls 18 may have provisions for allowing the operator to communicate to power-system controls 18 information received from position-information system 39 about the location of machine 10. For example, operator interface 42 may include components that the operator may use to feed information about the location of machine 10 to power-system controls 18.

Additionally, in some embodiments, power-system controls 18 may incorporate one or more components of position-information system 39. In some such embodiments, power-system controls 18 may interact with the off-board portion 47 of position-information system 39 to generate information about the location of machine 10.

Power system 12 is not limited to the configuration shown in FIG. 1. For example, electric power sources 16 may omit one or more of generator units G_(A), G_(B), G_(C) or include other generator units in addition to generator units G_(A), G_(B), G_(C). Additionally, one or more of generator units G_(A), G_(B), G_(C) may have fewer or more than two electric generators drivingly connected to their power source PS_(A), PS_(B), PS_(C). Furthermore, electric power loads 14 may include different numbers and/or types of components than shown in FIG. 1. For example, electric power loads 14 may include more or fewer electric propulsion motors 20 than shown in FIG. 1. In some embodiments, power system 12 may omit electric propulsion motors 20 altogether. In some such embodiments, power system 12 may not be part of a mobile machine. Moreover, power-transfer system 17 may have a different configuration than shown in FIG. 1. In some embodiments, power-transfer system 17 may not electrically isolate electric propulsion motors 20 from the other electric power loads 14 of machine 10.

Power-system controls 18 may also have a different configuration than shown in FIG. 1. For example, power-system controls 18 may have a different combination of controllers than shown in FIG. 1 for controlling generation and supply of electricity. Similarly, in addition to, or in place of, one or more of power-source controllers C_(PSA), C_(PSB), C_(PSC), controller 38, and controller 40, power-system controls 18 may include other types of control components, such as hardwired control circuits. Additionally, operator interface 42 may have a different configuration than the example provided in FIG. 1. Operator interface 42 may, for example, have different types of components that an operator can employ to indicate how he desires power system 12 to propel machine 10. In embodiments where machine 10 is not a mobile machine, operator interface 42 may omit such components altogether. Furthermore, operator interface 42 may omit mode selector 48.

INDUSTRIAL APPLICABILITY

Power system 12 may have application for any task requiring power. For example, in embodiments where machine 10 is a mobile machine and power system 12 includes electric propulsion motors 20, power system 12 may have application for propelling machine 10 to accomplish various tasks. Where machine 10 is a railroad locomotive, power system 12 may serve the purpose of propelling machine 10 to move railroad cars. To propel machine 10, power system 12 may run one or more of generator units G_(A), G_(B), G_(C) and supply electricity from one or more of electric generators EG_(A1), EG_(B1), E_(C1) of the one or more running generator units G_(A), G_(B), G_(C) to electric propulsion motors 20.

In addition to propelling machine 10 with electric propulsion motors 20, power system 12 may serve various other purposes with the second set of electric power loads 26. For example, with the second set of electric power loads 26, power system 12 may provide light, heating, cooling, compressed air, pump fluids, and/or move various components of machine 10. To accomplish such tasks, power-system controls 18 may run one or more of generator units G_(A), G_(B), G_(C) and supply electricity from one or more of electric generators EG_(A2), EG_(B2), EG_(C2) of the one or more running generator units G_(A), G_(B), G_(C) to the second set of electric power loads 26

In some embodiments and/or circumstances, the first set of electric power loads 24 may require electricity with one or more different characteristics from the electricity required by the second set of electric power loads 26. Meeting such a need may prove relatively straightforward with each generator unit G_(A), G_(B), G_(C) having one electric generator EG_(A1), EG_(B1), EG_(C1) associated with the first set of electric power loads 24 and a separate electric generator EG_(A2), EG_(B2), EG_(C2) associated with the second set of electric power loads 26. With this configuration, power system 12 may readily use electric generators EG_(A1), EG_(B1), EG_(C1) to supply to the first set of electric power loads 24 electricity that has one or more characteristics different from the electricity supplied to the second set of electric power loads 26 with electric generators EG_(A2), EG_(B2), EG_(C2).

For purposes of this disclosure, the electricity supplied to the first set of electric power loads 24 and the electricity supplied to the second set of electric power loads 26 have one or more different characteristics if they have different voltages and/or one or more different time-based characteristics. Time-based characteristics include whether the electricity is DC or AC and, if it is AC, the phase and frequency of the electricity. In some embodiments, power-system controls 18 may regulate the voltage of the electricity supplied to the second set of electric power loads 26 with power regulators PR_(A2), PR_(B2), PR_(C2) while allowing the voltage of electricity supplied to the first set of electric power loads 24 to vary dependent on the speed of electric propulsion motors 20.

In order to control generator units G_(A), G_(B), G_(C) to meet the needs of electric power loads 14, power-system controls 18 may monitor one or more electricity requirements of electric power loads 14 during operation of power system 12. For purposes of this disclosure, the term “electricity requirement” may refer to either a quantity of electric power required or a quantity of electric current required. The term “quantity of electric power” refers to the product of a quantity of electric current and the voltage at which the electric current is supplied, whereas the term “quantity of electric current” refers to the magnitude of the electric current without regard to the voltage at which it is supplied. Controller 40 may, for example, determine the aggregate quantity of electric power required by the second set of electric power loads 26 and the aggregate quantity of electric current required by the second set of electric power loads 26. Controller 40 may do so with information about electricity flowing in one or more portions of circuit 30 and/or with information about the operating states of one or more of the members of the second set of electric power loads 26.

Power-system controls 18 may determine one or more electricity requirements of the first set of electric power loads 24 based at least in part on operator inputs related to the desired propulsion of machine 10 with electric propulsion motors 20. For example, controller 40 may determine the quantity of power required by electric propulsion motors 20 based on the signal received from reverser 44 and the signal received from power selector 46. If the signal from reverser 44 indicates that the operator has selected the NEUTRAL operating state, controller 40 may determine that electric propulsion motors 20 do not require power. If the signal from reverser 44 indicates that the operator has selected either the FORWARD or REVERSE operating states, controller 40 may determine the quantity of electric power required by electric propulsion motors 20 based on which power setting of power selector 46 the operator has selected. For example, controller 40 may use a lookup table that indicates the quantity of electric power required by electric propulsion motors 20 for each respective power setting. For each successively higher power setting, electric propulsion motors 20 may require a higher quantity of electric power.

Power-system controls 18 may also determine the aggregate quantity of electric current required by electric propulsion motors 20. Controller 40 may compute the aggregate quantity of electric current required for electric propulsion motors 20 by dividing the aggregate quantity of electric power that the electric propulsion motors 20 require by the voltage of the electricity supplied to electric propulsion motors 20. In embodiments where power-system controls 18 allow the voltage of the electricity supplied to electric propulsion motors 20 to vary dependent on the speed of electric propulsion motors 20, controller 40 may employ various means to determine the voltage of electricity supplied to electric propulsion motors 20. Controller 40 may determine the voltage directly with voltage sensor 52. Alternatively, controller 40 may determine the voltage using the speed of machine 10, as sensed by speed sensor 50, and a known relationship between the speed of machine 10 and the voltage of electricity supplied to electric propulsion motors 20.

Based on the determined electricity requirements of electric power loads 14, power-system controls 18 may automatically control which of generator units G_(A), G_(B), G_(C) run. FIGS. 2A-2E illustrate one embodiment of a control method that power-system controls 18 may employ to ensure that generator units G_(A), G_(B), G_(C) meet the electricity requirements of machine 10 while balancing usage of generator units G_(A), G_(B), G_(C). FIG. 2A gives an overview of the high-level processes of the control method, and each of FIGS. 2B-2E provides details of one of the high-level processes shown in FIG. 2A. As FIG. 2A shows, initially, power-system controls 18 may set a priority ranking for generator units G_(A), G_(B), G_(C) (step 54). This may involve designating one of generator units G_(A), G_(B), G_(C) as a first priority generator unit, designating another of the generator units G_(A), G_(B), G_(C) as a second priority generator unit, and designating the remaining generator unit G_(A), G_(B), G_(C) as a third priority generator unit. As discussed below, in some circumstances, power-system controls 18 may exclude one or more of generator units G_(A), G_(B), G_(C) from the priority ranking for various reasons.

After setting the priority ranking, power-system controls 18 may determine whether to operate in switcher mode or line-haul mode (step 56). Power-system controls 18 may, for example, determine whether to operate in switcher mode or line-haul mode based on whether the operator of machine 10 has selected switcher mode or line-haul mode with mode selector 48. In some circumstances and/or embodiments, power-system controls 18 may use additional or alternative factors to determine whether to operate in switcher mode or line-haul mode. For example, power-system controls 18 may determine whether to operate in switcher mode or line-haul mode based on information about the location of machine 10, which information may come from position-information system 39. In some embodiments, power-system controls 18 may automatically select switcher mode in response to information indicating that machine 10 is in a railyard, and power-system controls 18 may automatically select line-haul mode to information indicating that machine 10 is not in a railyard. If power-system controls 18 select the switcher mode of operation, power-system controls 18 may control which of generator units G_(A), G_(B), G_(C) run based on their priority ranking and a first control algorithm (step 58). On the other hand, if power-system controls 18 select the line-haul mode of operation, power-system controls 18 may control which of generator units G_(A), G_(B), G_(C) run based on their priority ranking and a second control algorithm (step 60).

Both the first control algorithm (step 58) and the second control algorithm (step 60) may involve running a generator unit G_(A), G_(B), G_(C) with a higher position in the priority ranking in preference to a generator unit G_(A), G_(B), G_(C) with a lower position in the priority ranking. For example, in circumstances that warrant running only one generator unit G_(A), G_(B), G_(C), power-system controls 18 may run the first priority generator unit G_(A), G_(B), G_(C) in preference to the second and third priority generator units G_(A), G_(B), G_(C). Similarly, in circumstances that warrant running two of generator units G_(A), G_(B), G_(C), power-system controls 18 may run the first priority generator unit G_(A), G_(B), G_(C) and the second priority generator unit G_(A), G_(B), G_(C) in preference to the third priority generator unit G_(A), G_(B), G_(C).

While controlling which of generator units G_(A), G_(B), G_(C) run based on either the first or second control algorithm, power-system controls 18 may repeatedly determine whether predetermined conditions that serve as a trigger for resetting the priority ranking exist (step 62). Power-system controls 18 may reset the priority ranking each time these predetermined conditions arise. Predetermined conditions that power-system controls 18 may use as a trigger for resetting the priority ranking are discussed in more detail below in connection with FIG. 2D.

FIG. 2B illustrates one embodiment of the first control algorithm (step 58, FIG. 2A) for controlling which generator units G_(A), G_(B), G_(C) run when the operator has the selected the switcher mode of operation. Upon initiating control according to the first control algorithm, power-system controls 18 may run all of the generator units G_(A), G_(B), G_(C) in the priority ranking (step 64), regardless of the electricity requirements of power system 12.

The first control algorithm may also involve, after initially running all of the generator units G_(A), G_(B), G_(C) in the priority ranking, stopping one or more of the running generator units G_(A), G_(B), G_(C) if predetermined operating conditions related to the electricity requirements of power system 12 over a period of time occur. For example, as FIG. 2B shows, power-system controls 18 may stop one or more of the running generator units if an electricity requirement of power system 12 remains below a reference value for a reference period of time. Accordingly, after starting the first control algorithm with all of the generator units G_(A), G_(B), G_(C) in the priority ranking running, power-system controls 18 may determine whether an electricity requirement of power system 12 falls below the reference value (step 66). Power-system controls 18 may, for example, determine whether the aggregate quantity of electric power required by the first set of electric power loads 24 (electric propulsion motors 20) falls below 250 kW. If power-system controls 18 determine that the electricity requirement does not fall below the reference value (step 66), power-system controls .18 may continue running all of generator units G_(A), G_(B), G_(C) indefinitely (step 64).

If power-system controls 18 determine that the electricity requirement falls below the reference value, power-system controls 18 may run a timer (step 68). After starting the timer in response to the electricity requirement falling below the reference value, power-system controls 18 may determine whether the elapsed time of the timer exceeds a reference period of time (step 70). If the elapsed time of the timer does not exceed the reference period of time, power-system controls 18 may continue running all of the generator units G_(A), G_(B), G_(C) in the priority ranking (step 64) and repeatedly check whether the electricity requirement remains below the reference value (step 66). If the electricity requirement remains below the reference value long enough for the elapsed time of the timer to exceed the reference period of time (step 70), power-system controls 18 may stop all of generator units G_(A), G_(B), G_(C) except the generator unit G_(A), G_(B), G_(C) with the first priority ranking (step 72).

After stopping all of the generator units G_(A), G_(B), G_(C) except the generator unit G_(A), G_(B), G_(C) with the first priority ranking, power-system controls 18 may check to see if the electricity requirement has risen above the reference value (step 74). If not, power-system controls 18 may continue running only the generator unit G_(A), G_(B), G_(C) with the first priority ranking (step 76). If the electricity requirement does rise back above the reference value (step 74), power-system controls 18 may resume running all of the generator units G_(A), G_(B), G_(C) in the priority ranking (step 64) and monitoring whether the electricity requirement falls below the reference value (step 66).

Employing such an algorithm for controlling which of generator units G_(A), G_(B), G_(C) run when the operator has selected the switcher mode of operation may provide a number of performance advantages. Initially running all of the generator units G_(A), G_(B), G_(C) included in the priority ranking may allow power system 12 to effectively meet abrupt increases in electricity requirements because increasing the output of the running generator units G_(A), G_(B), G_(C) takes relatively little time compared to starting additional generator units G_(A), G_(B), G_(C). This may prove valuable where machine 10 is a locomotive and the operator uses machine 10 to move railroad cars in a railyard because this task may involve frequent abrupt changes in the quantity of electricity supplied to electric propulsion motors 20. Stopping one or more of generator units G_(A), G_(B), G_(C) if and only if the electricity requirement remains low for an extended period may avoid unnecessary fuel consumption and wear of generator units G_(A), G_(B), G_(C) during inactive periods without unduly compromising performance during active periods.

The first control algorithm is not limited to the examples discussed in connection with FIG. 2B. Power-system controls 18 may use different and/or additional criteria for determining whether to stop and/or restart one or more of generator units G_(A), G_(B), G_(C). In some embodiments, power-system controls 18 may use information about the location of machine 10, which may come from position-information system 39, as a factor in determining whether to stop and/or restart one or more of generator units G_(A), G_(B), G_(C). For example, in response to information indicating that machine 10 is in an area for which there are laws regulating when and/or how long engines can idle, power-system controls 18 may respond by controlling generator units G_(A), G_(B), G_(C) in a manner complying with such laws. Additionally, rather than either running all of generator units G_(A), G_(B), G_(C) in the priority ranking or only one of generator units G_(A), G_(B), G_(C), power-system controls 18 may stop and/or restart the generator units G_(A), G_(B), G_(C) in stages as the electricity requirements of power system 12 change.

FIG. 2C illustrates one embodiment of the second control algorithm (step 60, FIG. 2A) for use in controlling which generator units G_(A), G_(B), G_(C) run when the operator has selected the line-haul mode of operation. When executing the second control algorithm, power-system controls 18 may identify a first set of one or more of generator units G_(A), G_(B), G_(C) based on the priority ranking and the quantity of electric current required by the first set of electric power loads 24 (step 78, FIG. 2C). For the first set of one or more of generator units G_(A), G_(B), G_(C), power-system controls 18 may identify one or more generator units G_(A), G_(B), G_(C) whose first electric generators EG_(A1), EG_(B1), EG_(C1) have an aggregate electric current capacity at least equal to the quantity of electric current required by the first set of electric power loads 24. That way, the one or more generator units G_(A), G_(B), G_(C) identified for the first set can meet the electric current requirement of the first set of electric power loads 24.

Power-system controls 18 may use various approaches to identify a set of one or more of generator units G_(A), G_(B), G_(C) capable of at least meeting the electric current requirement of the first set of electric power loads 24. In some embodiments, power-system controls 18 may employ a lookup table that identifies for any given quantity of electric current required by the first set of electric power loads 24 a set of one or more of generator units G_(A), G_(B), G_(C) capable of at least meeting that electric current requirement. FIG. 3A shows one embodiment of such a lookup table. Consider, as an example, circumstances where power-system controls 18 employ the lookup table of FIG. 3A and the first set of electric power loads 24 requires 2, 000 amps of electric current. In such circumstances, power-system controls 18 may include in the first set of one or more of generator units G_(A), G_(B), G_(C) the generator units G_(A), G_(B), G_(C) with the first and second priority rankings, but not the generator unit G_(A), G_(B), G_(C) with the third priority ranking.

Power-system controls 18 may also use a lookup table, such as the one shown in FIG. 3A, to determine how much electric current each generator unit G_(A), G_(B), G_(C) in the first set should supply to the first set of electric power loads 24. Consider again the case where the first set of electric power loads 24 requires 2,000 amps of electric current. In such circumstances, power-system controls 18 may use the lookup table of FIG. 3A to determine that the first and second priority generator units G_(A), G_(B), G_(C) should supply 1, 250 amps and 750 amps, respectively, to the first set of electric power loads 24.

In addition to identifying the first set of one or more of generator units G_(A), G_(B), G_(C), power-system controls 18 may identify a second set of one or more of generator units G_(A), G_(B), G_(C) based on the priority ranking and the quantity of electric current required by the second set of electric power loads 26 (step 80). For the second set of one or more of generator units G_(A), G_(B), G_(C), power-system controls 18 may identify one or more generator units G_(A), G_(B), G_(C) whose second electric generators EG_(A2), EG_(B2), EG_(C2) have an aggregate electric current capacity at least equal to the quantity of electric current required by the second set of electric power loads 26. That way, the generator units G_(A), G_(B), G_(C) identified for the second set can meet the electric current requirement of the second set of electric power loads 26. As will become clear from the example provided below, the second set of one or more of generator units G_(A), G_(B), G_(C) may include some or all of the generator units G_(A), G_(B), G_(C) identified for the first set of one or more of generator units G_(A), G_(B), G_(C).

Power-system controls 18 may employ a variety of processes to identify a set of one or more of generator units G_(A), G_(B), G_(C) capable of at least meeting the electric current requirement of the second set of electric power loads 26. In some embodiments, power-system controls 18 may use a lookup table that identifies, for any given quantity of electric current required by the second set of electric power loads 26, a set of one or more of generator units G_(A), G_(B), G_(C) capable of supplying at least that much electric current thereto. FIG. 3B shows such a lookup table. Consider, as an example, circumstances where power-system controls 18 employ the lookup table of FIG. 3B and the second set of electric power loads 26 requires 750 amps of electric current. In such circumstances, power-system controls 18 may include in the second set of one or more of generator units G_(A), G_(B), G_(C) the generator unit G_(A), G_(B), G_(C) with the first priority ranking, but not the generator units G_(A), G_(B), G_(C) with the second and third priority rankings. Similar to the lookup table of FIG. 3A, the lookup table of FIG. 3B may also serve as a means for determining how much of the electric current required by the second set of electric power loads 26 each generator unit G_(A), G_(B), G_(C) of the second set of generator units G_(A), G_(B), G_(C) should supply.

In addition to the first and second sets of one or more of generator units G_(A), G_(B), G_(C), power-system controls 18 may identify a third set of one or more of generator units G_(A), G_(B), G_(C) based on the priority ranking and the aggregate quantity of electric power required by the first and second sets of electric power loads 24, 26 (step 82, FIG. 2C). For the third set of one or more of generator units G_(A), G_(B), G_(C), power-system controls 18 may identify one or more generator units G_(A), G_(B), G_(C) with an aggregate power capacity at least equal to the aggregate quantity of electric power required by the first and second sets of electric power loads 24, 26. That way, the one or more generator units G_(A), G_(B), G_(C) identified for the third set will have sufficient power capacity to meet the power requirements of power system 12. Just as the first set and the second set of one or more of generator units G_(A), G_(B), G_(C) may overlap, the third set of one or more of generator units G_(A), G_(B), G_(C) may include one or more of the same generator units G_(A), G_(B), G_(C) as the first set and/or the second set.

Power-system controls 18 may implement various methods of identifying a set of one or more of generator units G_(A), G_(B), G_(C) with an aggregate power capacity at least equal to the aggregate quantity of power required by the first and second sets of electric power loads 24, 26. In some embodiments, power-system controls 18 may employ a lookup table, such as the lookup table shown in FIG. 3C, that identifies, for any given aggregate quantity of electric power required, a set of one or more of generator units G_(A), G_(B), G_(C) with at least that much aggregate power capacity. Consider, as an example, circumstances where power-system controls 18 employ the lookup table of FIG. 3C and the aggregate quantity of electric power required is 250 kW. In such circumstances, power-system controls 18 may include in the third set of one or more of generator units G_(A), G_(B), G_(C) the generator unit G_(A), G_(B), G_(C) with the first priority ranking, but not the generator units G_(A), G_(B), G_(C) with the second and third priority rankings. Similar to the lookup table of FIGS. 3A and 3B, the lookup table of FIG. 3C may also indicate how to divide the power load amongst the generator units G_(A), G_(B), G_(C) of the third set.

Returning to FIG. 2C, power-system controls 18 may run each generator unit G_(A), G_(B), G_(C) of the first set, each generator unit G_(A), G_(B), G_(C) of the second set, and each generator unit G_(A), G_(B), G_(C) of the third set (step 84). For example, in the exemplary case where the first set includes the first and second priority generator units G_(A), G_(B), G_(C), the second set includes the first priority generator unit G_(A), G_(B), G_(C), and the third set includes the first priority generator unit G_(A), G_(B), G_(C), power-system controls 18 may run the first and second priority generator units G_(A), G_(B), G_(C).

While executing the second algorithm for controlling which of generator units G_(A), G_(B), G_(C) run, power-system controls 18 may repeatedly reevaluate which generator units G_(A), G_(B), G_(C) each of the first, second, and third sets of one or more of generator units G_(A), G_(B), G_(C) should include. Accordingly, as the electricity requirements of the various electric power loads 14 change, power-system controls 18 may add one or more of generator units G_(A), G_(B), G_(C) and/or remove one or more of generator units G_(A), G_(B), G_(C) from the first set, the second set, and/or the third set. As the composition of the first set, the second set, and/or the third set changes, power-system controls 18 may start and/or stop one or more of generator units G_(A), G_(B), G_(C) accordingly.

In some embodiments, when one or more electricity requirements of power system 12 approach the capacity of the running generator units G_(A), G_(B), G_(C) to meet those electricity requirements, power-system controls 18 may start one or more additional generator units G_(A), G_(B), G_(C) to prepare for further load increase. For example, referring to FIG. 3A, when the quantity of electric current required by the first set of electric power loads 24 reaches 1,300 amps, it may approach the capacity of the first priority generator unit G_(A), G_(B), G_(C) to supply electric current thereto. Accordingly, when this occurs, power-system controls 18 may add the second priority generator unit G_(A), G_(B), G_(C) to the first set of one or more of generator units G_(A), G_(B), G_(C) and start the second priority generator unit G_(A), G_(B), G_(C). This may prepare power system 12 to quickly meet the electricity requirements of the first set of electric power loads 24 if the quantity of electric current required by the first set of electric power loads 24 rises beyond the capacity of the first priority generator unit G_(A), G_(B), G_(C) to supply electric current thereto. Power-system controls 18 may similarly start an additional generator unit G_(A), G_(B), G_(C) when the quantity of electric current required by the second set of electric power loads 26 or the aggregate quantity of electric power required approaches the associated capacity of the running generator units G_(A), G_(B), G_(C.)

Executing the second algorithm for controlling which of generator units G_(A), G_(B), G_(C) run may provide a number of advantages. Using electric current requirements and electric power requirements as separate factors may allow power-system controls 18 to control which generator units G_(A), G_(B), G_(C) run in a manner that ensures meeting the electricity requirements of electric power loads 14 in widely varying circumstances. Using electric current requirements as a factor may help ensure that power-system controls 18 run enough of generator units G_(A), G_(B), G_(C) to meet the needs of electric power loads 14 in circumstances requiring a large quantity of electric current but a low quantity of electric power. Conversely, using electric power requirements as a factor may help ensure that power-system controls 18 run enough of generator units G_(A), G_(B), G_(C) to meet the needs of electric power loads 14 in circumstances requiring a large quantity of electric power but a low quantity of electric current.

Additionally, the second algorithm accommodates constructing each of generator units G_(A), G_(B), G_(C) with one electric generator EG_(A1), EG_(B1), EG_(C1) for the first set of electric power loads 24 and a separate electric generator EG_(A2), EG_(B2), EG_(C2) for the second set of electric power loads 26 while reliably meeting the electricity requirements of all electric power loads 14. The second control algorithm achieves this benefit by using an electricity requirement of the first set of electric power loads 24 and an electricity requirement of the second set of electric power loads 26 as separate factors in determining which of generator units G_(A), G_(B), G_(C) run. By doing so, the second control algorithm may ensure that the running generator units G_(A), G_(B), G_(C) have sufficient generating capacity for each of the first and second sets of electric power loads 24, 26.

The second control algorithm is not limited to the examples discussed above. For instance, power-system controls 18 may use values other than those shown in FIGS. 3A-3C as the criteria for determining which of generator units G_(A), G_(B), G_(C) to include in the first, second, and third sets of one or more of generator units G_(A), G_(B), G_(C). Additionally, power-system controls 18 may forgo expressly identifying the first, second, and third sets of one or more of generator units G_(A), G_(B), G_(C). Instead, power-system controls 18 may use the quantities of electric current required by the first and second sets of electric power loads 24, 26 and the aggregate quantity of electric power required as factors in other methods of controlling which of generator units G_(A), G_(B), G_(C) run to meet all of the electricity requirements of power system 12. For example, power-system controls 18 may use a single lookup table that identifies which of generator units G_(A), G_(B), G_(C) to run for any given quantity of electric current required by the first set of electric power loads 24, quantity of electric current required by the second set of electric power loads 26, and aggregate quantity of electric power required. Furthermore, power-system controls 18 may employ means other than lookup tables, such as equations, to determine which of generator units G_(A), G_(B), G_(C) to run.

Additionally, power-system controls 18 may determine which of generator units G_(A), G_(B), G_(C) to run based on different parameters than those discussed above. Power-system controls 18 may use other parameters in combination with the quantity of electric current required by the first set of electric power loads 24, the quantity of electric current required by the second set of electric power loads 26, and the aggregate quantity of electric power required. Additionally, power-system controls 18 may forgo using one or more of the parameters discussed above as factors in determining which of generator units G_(A), G_(B), G_(C) to run. In some embodiments, power-system controls 18 may determine which of generator units G_(A), G_(B), G_(C) to run based on a single parameter related to the electricity requirements of electric power loads 14, such as the aggregate quantity of electric power required by electric power loads 14.

In some embodiments, power-system controls 18 may use information about the position of machine 10, which may come from position-information system 39, as a factor in controlling these aspects of the operation of power system 12. For example, power-system controls 18 may use information about the location of machine 10 to select one or more lookup tables or equations for use in determining which of generator units G_(A), G_(B), G_(C) to run. Similarly, power-system controls 18 may use one or more lookup tables and/or equations that include information about the location of machine 10 as a factor in determining which of generator units G_(A), G_(B), G_(C) to run. When executing the second control algorithm, power-system controls 18 may advantageously use information about the location of machine 10 as a factor in controlling which of generator units G_(A), G_(B), G_(C) to tailor operation of power-system 12 in various ways to the location of machine 10. For example, power-system controls 18 may use such location information to tailor operation of power system 12 for hilly or flat terrain. Similarly, power-system controls 18 may use such location information to tailor operation of power system 12 to local laws, such as laws regulating emission of noise and/or pollutants.

Returning to FIG. 2A, as noted above, while executing the first or second control algorithm, power-system controls 18 may repeatedly determine whether predetermined conditions that serve as a trigger for resetting the priority ranking of generator units G_(A), G_(B), G_(C) exist (step 62). Power-system controls 18 may implement various approaches for doing so. In some embodiments, the criteria used by power-system controls 18 to determine whether to reset the priority ranking may advance the objectives of balancing the amount of service accumulated by different generator units G_(A), G_(B), G_(C) and limiting or precluding operation of malfunctioning generator units G_(A), G_(B), G_(C). For example, power-system controls 18 may advance these objectives by using the , method shown in FIG. 2D to determine whether to reset the priority ranking.

In this method, power-system controls 18 may determine whether the amount of service accumulated by any generator unit G_(A), G_(B), G_(C) since a reference point in time exceeds a reference value (step 86). For this determination, power-system controls 18 may use various parameters as an indication of the amount of service accumulated by each generator unit G_(A), G_(B), G_(C), various events as the reference point in time, and various values as the reference value. In some embodiments, power-system controls 18 may measure accumulated service of each generator unit G_(A), G_(B), G_(C) using a parameter that indicates the actual quantity of work done (the number of units of energy produced) by the generator unit G_(A), G_(B), G_(C), rather than just the number of operating hours. For example, power-system controls 18 may use the quantity of fuel consumed or the quantity of electricity generated by each generator unit G_(A), G_(B), G_(C) as a measure of the amount of service the generator unit G_(A), G_(B), G_(C) has accumulated.

For the reference point in time from which to measure the amount of service accumulated by each generator unit G_(A), G_(B), G_(C), power-system controls 18 may, in some embodiments, use an event other than the first time each generator unit G_(A), G_(B), G_(C) ran. For example, power-system controls 18 may use the last time the priority ranking was set as the reference point in time. Thus, step 86 may involve, for example, determining whether any one of generator units G_(A), G_(B), G_(C) has consumed a quantity of fuel greater than the reference value or generated a quantity of electricity greater than the reference value since the priority ranking was last set. Circumstances where one of generator units G_(A), G_(B), G_(C) has accumulated an amount of service greater than the reference value since the reference point in time may warrant resetting the priority ranking to help balance usage between the different generator units G_(A), G_(B), G_(C).

If power-system controls 18 make a negative determination at step 86, power-system controls 18 may also determine whether any of generator units G_(A), G_(B), G_(C) currently have a condition that makes operation unacceptable or undesirable (step 88). Conditions that may make operation of a generator unit G_(A), G_(B), G_(C) unacceptable may include, for example, a complete failure of a lubrication or cooling system of the generator unit G_(A), G_(B), G_(C). Conditions that may make operation of a generator unit G_(A), G_(B), G_(C) undesirable may include, for example, an undesirable operating state of a lubrication or cooling system not amounting to a complete failure. Conditions making operation of one or more generator units G_(A), G_(B), G_(C) unacceptable or undesirable may warrant resetting the priority ranking to reduce the rank of those generator units G_(A), G_(B), G_(C) or exclude them from the priority ranking altogether.

If power-system controls 18 make an affirmative determination at step 86 or 88, power-system controls 18 may determine whether all of generator units G_(A), G_(B), G_(C) are idling or stopped and the operator has selected the NEUTRAL operating state of reverser 44 (step 90). If so, power-system control 18 may elect to reset the priority ranking (step 92).

On the other hand, if power-system controls 18 make a negative determination at both of steps 86 and 88 or at step 90, power-system controls 18 may forgo resetting the priority ranking (step 94). Negative determinations at both of steps 86 and 88 may indicate that conditions do not warrant resetting the priority ranking. A negative determination at step 90 may indicate that the operator may have a critical need for propulsion power at any time. Accordingly, in such circumstances, power-system controls 18 may forgo resetting the priority ranking and focus on controlling generator units G_(A), G_(B), G_(C) to ensure meeting the operator's needs for propulsion power.

Criteria that power-system controls 18 may use to determine when to reset the priority ranking of generator units G_(A), G_(B), G_(C) are not limited to the examples discussed above in connection with FIG. 2D. For example, in some embodiments, power-system controls 18 may disregard whether all of generator units G_(A), G_(B), G_(C) are stopped or idling when determining whether to reset the priority ranking. In such embodiments, power-system controls 18 may reset the priority ranking while one or more of generator units G_(A), G_(B), G_(C) are running at a power level above idle. This may result in power-system controls 18 starting one or more generator units G_(A), G_(B), G_(C) that have risen in the priority ranking and stopping one or more of the generator units G_(A), G_(B), G_(C) that have fallen in the priority ranking. Power-system controls 18 may do so without interrupting power supply to electric power loads 14 by simultaneously initiating supply of electricity from the newly started generator units G_(A), G_(B), G_(C) and discontinuing supply of electricity from the generator units G_(A), G_(B), G_(C) selected to stop running.

When power-system controls 18 do set the priority ranking of generator units G_(A), G_(B), G_(C) (step 54, FIG. 2A), power-system controls 18 may use various control methods to do so. FIG. 2E illustrates one control method that power-system controls 18 may use when setting the priority ranking of generator units G_(A), G_(B), G_(C). Power-system controls 18 may first identify which of generator units G_(A), G_(B), G_(C) are available for inclusion in the priority ranking (step 96). Power-system controls 18 may consider unavailable for inclusion in the priority ranking any generator units G_(A), G_(B), G_(C) having conditions that make their operation unacceptable. Additionally, if the operator of machine 10 has used service interface 43 to command power-system controls 18 to exclude any of generator units G_(A), G_(B), G_(C) from operation, power-system controls 18 may consider each of those generator units G_(A), G_(B), G_(C) unavailable for inclusion in the priority ranking.

After identifying which of generator units G_(A), G_(B), G_(C) are available for inclusion in the priority ranking, power-system controls 18 may determine whether any of those generator units G_(A), G_(B), G_(C) have conditions that make operating them undesirable (step 98). If not, power-system controls 18 may rank all of the available generator units G_(A), G_(B), G_(C) in reverse order of the amount of service each has accumulated since the same reference point in time that power-system controls 18 used to determine whether to reset the priority ranking (step 100). In other words, power-system controls 18 may give the first priority ranking to the generator unit G_(A), G_(B), G_(C) that has accumulated the least amount of service since the reference point in time, give the second priority ranking to the generator unit G_(A), G_(B), G_(C) that has accumulated the second lowest amount of service since the reference point in time, and so on.

When ranking each generator unit G_(A), G_(B), G_(C) in the priority ranking, power-system controls 18 may, in some embodiments, measure the accumulated service of each generator unit G_(A), G_(B), G_(C) with the same parameter and from the same reference point in time as used in step 86 (FIG. 2D) in determining whether to reset the priority ranking. Thus, power-system controls 18 may, for example, measure the accumulated service of each generator unit G_(A), G_(B), G_(C) with a parameter that indicates the quantity of work done (number of units of energy produced) by the generator unit G_(A), G_(B), G_(C), such as the quantity of fuel consumed or the quantity of electricity generated. Similarly, power-system controls 18 may use the last time the priority ranking was set as the reference point in time from which the accumulated service of each generator unit G_(A), G_(B), G_(C) is measured when setting the priority ranking.

If power-system controls 18 determine that one or more generator units G_(A), G_(B), G_(C) have conditions that make operating them undesirable (step 98, FIG. 2E), power-system controls 18 may employ a slightly different approach to setting the priority ranking. In such circumstances, power-system controls 18 may place in a first class all of the available generator units G_(A), G_(B), G_(C) that do not have a condition that would make operating them undesirable (step 102). Power-system controls 18 may place in a second class all of the available generator units G_(A), G_(B), G_(C) having conditions that make operating them undesirable (step 104). Power-system controls 18 may then fill the highest positions in the priority ranking with the generator units G_(A), G_(B), G_(C) from the first class ranked in reverse order of the amount of service each has accumulated since the reference point in time (step 106). Subsequently, starting with the rank immediately below the lowest ranked generator unit G_(A), G_(B), G_(C) of the first class, power-system controls 18 may rank the generator units G_(A), G_(B), G_(C) of the second class in reverse order of the amount of service each has accumulated since the reference point in time (step 108).

After establishing the order of all available generator units G_(A), G_(B), G_(C) in the priority ranking (step 100 or steps 106, 108), power-system controls 18 may reset the reference point in time that power-system controls 18 will use to determine whether to reset the priority ranking (step 101). For example, power-system controls 18 may reset the reference point in time to the time at which power-system controls 18 just finished setting the priority ranking.

With the above-discussed methods of setting and resetting a priority ranking of generator units G_(A), G_(B), G_(C) and using the priority ranking to determine which generator units G_(A), G_(B), G_(C) to run, power-system controls 18 may effectively balance usage of the different generator units G_(A), G_(B), G_(C) while meeting the electricity needs of power system 12. Setting a priority ranking for the generator units G_(A), G_(B), G_(C) based on the amount of service each has accumulated over a preceding period may enable evening the service accumulated by the different generator units G_(A), G_(B), G_(C) by preferentially using generator units G_(A), G_(B), G_(C) with higher rank. Additionally, by only resetting the priority ranking when predetermined conditions arise, power-system controls 18 may avoid unnecessarily frequent changes in which of generator units G_(A), G_(B), G_(C) are running. Furthermore, setting the priority ranking based on a parameter that indicates the actual amount of work done by each generator unit G_(A), G_(B), G_(C) may balance the actual wear accumulated by the different generator units G_(A), G_(B), G_(C) better than using a parameter such as operating hours.

Additionally, using an event other than the time each generator unit G_(A), G_(B), G_(C) first ran as the reference point in time for setting the priority ranking may provide certain advantages. For example, this approach may prove beneficial in circumstances where one or more of generator units G_(A), G_(B), G_(C) have accumulated a large amount of service since they first ran and the operator replaces one or more of the generator units G_(A), G_(B), G_(C) with a new or nearly new unit. In such circumstances, if power-system controls 18 used the first time each generator unit G_(A), G_(B), G_(C) ran as the reference point for setting the priority ranking, the new or nearly new generator unit G_(A), G_(B), G_(C) could end up with the first priority ranking every time initially. This could result in the new or nearly new generator unit G_(A), G_(B), G_(C) accumulating much more service in the short run, which could force the operator to service the new or nearly new generator unit G_(A), G_(B), G_(C) more frequently than if power-system controls 18 balance the usage of all of generator units G_(A), G_(B), G_(C) in the short term. Power-system controls 18 may balance short-term usage of each generator unit G_(A), G_(B), G_(C) effectively by setting the priority ranking based on the amount of service accumulated by each generator unit G_(A), G_(B), G_(C) since some event closer in time than the first time each generator unit G_(A), G_(B), G_(C) ran.

Methods of controlling power system 12 are not limited to the examples discussed above in connection with FIGS. 2A-2E and 3A-3C. Power-system controls 18 may use the principles of the control methods disclosed above to control more than or less than three generator units G_(A), G_(B), G_(C). Additionally, in controlling which of generator units G_(A), G_(B), G_(C) run, power-system controls 18 may perform the actions discussed above in different orders, omit one or more of the actions discussed above, perform actions other than those discussed above, and/or perform one or more of the actions discussed above in different manners. In some embodiments, such as embodiments where operator interface 42 omits mode selector 48, power-system controls 18 may use the same control algorithm for determining which of generator units G_(A), G_(B), G_(C) run in all circumstances, rather than selecting between the first and second control algorithms discussed above. Alternatively, in some embodiments, power-system controls 18 may have more than two control algorithms for determining which of generator units G_(A), G_(B), G_(C) to run in different circumstances.

Additionally, the methods of setting and resetting the priority ranking of generator units G_(A), G_(B), G_(C) are not limited to the examples discussed above. In some embodiments, power-system controls 18 may use additional criteria for determining the order of generator units G_(A), G_(B), G_(C) in the priority ranking. For example, in addition to the total amount of service accumulated by each generator unit G_(A), G_(B), G_(C) since the reference point in time, power-system controls 18 may use the amount of service accumulated by each generator unit G_(A), G_(B), G_(C) when operating at certain power levels, such as low power levels, as another factor in determining the priority ranking.

Additionally, power-system controls 18 may employ different techniques for addressing generator units G_(A), G_(B), G_(C) having conditions that make operating them unacceptable or undesirable. In some embodiments, for example, power-system controls 18 may place all of the generator units G_(A), G_(B), G_(C) in the priority ranking without regard to whether they have conditions that make operating them unacceptable or undesirable. In such embodiments, power-system controls 18 might control which of generator units G_(A), G_(B), G_(C) run by electing to run a generator unit G_(A), G_(B), G_(C) with a higher position in the priority ranking in preference to a generator unit G_(A), G_(B), G_(C) with a lower position in the priority ranking while skipping any generator units G_(A), G_(B), G_(C) having conditions making their operation unacceptable or undesirable. In such embodiments, power-system controls 18 might, for example, run generator units G_(A), G_(B), G_(C) having conditions that make operating them undesirable if the other generator units G_(A), G_(B), G_(C) have insufficient capacity to meet the electricity requirements of electric power loads 14.

Furthermore, in some embodiments, power-system controls 18 may use one set of criteria for setting the priority ranking one time and a different set of criteria for setting the priority ranking another time. For example, rather than always setting the priority ranking based on the amount of service accumulated by each generator unit G_(A), G_(B), G_(C) since the last time the priority ranking was set, power-system controls 18 may occasionally use a longer interval of service as the basis for the priority ranking or set the priority ranking randomly. Either of these techniques may help ensure that no one generator unit G_(A), G_(B), G_(C) perpetually receives the second priority ranking.

It will be apparent to those skilled in the art that various modifications and variations can be made in the power system and methods without departing from the scope of the disclosure. Other embodiments of the disclosed power system and methods will be apparent to those skilled in the art from consideration of the specification and practice of the power system and methods disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope of the disclosure being indicated by the following claims and their equivalents. 

1. A method of operating a power system of a railroad locomotive, the power system having power-system controls, the method comprising: automatically setting a priority ranking for a plurality of generator units of the power system of the locomotive with the power-system controls based at least in part on an operating parameter of each generator unit indicative of a quantity of energy the generator unit has produced; and automatically controlling which of the generator units run with the power- system controls based at least in part on the priority ranking of the generator units.
 2. The method of claim 1, wherein the operating parameter is a quantity of fuel consumed by each generator unit.
 3. The method of claim 1, wherein the operating parameter is a quantity of electricity generated by each generator unit.
 4. The method of claim 1, further including, subsequent to setting the priority ranking for the plurality of generator units, automatically resetting the priority ranking for the plurality of generator units in response to predetermined conditions.
 5. The method of claim 4, wherein automatically resetting the priority ranking in response to predetermined conditions includes automatically resetting the priority ranking in response to a quantity of the operating parameter for at least one of the generator units exceeding a reference value.
 6. The method of claim 4, wherein resetting the priority ranking includes resetting the priority ranking based on a quantity of the operating parameter for each generator unit measured from the time the priority ranking was set.
 7. The method of claim 1, wherein: the method further includes selectively propelling the railroad locomotive with power from one or more of the plurality of generator units.
 8. The method of claim 1, wherein automatically setting the priority ranking for the plurality of generator units with the power-system controls includes excluding one or more of the generator units from the priority ranking if an operator has transmitted to the power-system controls one or more predetermined communications for excluding one or more of the generator units from operation.
 9. A method of operating a power system of a railroad locomotive, the power system having power-system controls, the method comprising: automatically controlling with the power-system controls of the railroad locomotive which of a plurality of generator units of the power system run, including selecting which of the generator units run based at least in part on an operating parameter indicative of an amount of service accumulated by each generator unit since a reference point in time, the reference point in time being a time other than the time the generator unit first ran.
 10. The method of claim 9, further including resetting the reference point in time in response to predetermined conditions.
 11. The method of claim 10, wherein resetting the reference point in time in response to predetermined conditions includes resetting the reference point in time in response to a quantity of the operating parameter for one of the generator units exceeding a reference value.
 12. The method of claim 9, wherein selecting which of the generator units run based at least in part on an operating parameter indicative of an amount of service accumulated by each generator unit since a reference point in time includes setting a priority ranking for the plurality of generator units based at least in part on a quantity of the operating parameter for each generator unit; and when selecting a subset of the generator units to run, electing to run a generator unit with a higher position in the priority ranking over a generator unit with a lower position in the priority ranking.
 13. The method of claim 9, wherein the operating parameter is a quantity of fuel consumed by each generator unit since the reference point in time.
 14. The method of claim 9, wherein the operating parameter is a quantity of electricity generated by each generator unit since the reference point in time.
 15. A railroad locomotive, comprising: a plurality of generator units; one or more electric propulsion motors; power-system controls that control the plurality of generator units and the one or more electric propulsion motors, including selectively operating the mobile machine in a first operating mode, including, upon entering the first operating mode, running a plurality of the generator units regardless of the electricity requirements of the railroad locomotive; selectively operating the railroad locomotive in a second operating mode, including, whenever operating the railroad locomotive in the second operating mode, controlling which of the plurality of generator units run based at least in part on one or more parameters related to the electricity requirements of the railroad locomotive; and selectively propelling the railroad locomotive at least in part by operating one or more of the one or more electric propulsion motors with electricity generated by one or more of the plurality of generator units.
 16. The railroad locomotive of claim 15, wherein operating in the first operating mode further includes, after initially running a plurality of the generator units regardless of the electricity requirements of the railroad locomotive, stopping one or more of the plurality of running generator units if predetermined operating conditions related to the electricity requirements of the railroad locomotive over a period of time occur.
 17. The railroad locomotive of claim 15, wherein operating in the first operating mode further includes, after initially running a plurality of the generator units regardless of the electricity requirements of the railroad locomotive, stopping one or more of the plurality of running generator units if a parameter related to the electricity requirements of the railroad locomotive remains below a reference value for a reference period of time.
 18. The railroad locomotive of claim 17, wherein the parameter related to the electricity requirements of the railroad locomotive is a quantity of electric power required by the electric propulsion motors. 